The following code uses the replace() method of the String class in Java.

String a = "abc/xyz";
System.out.println(a.replace("/", "\\"));

/ in the given String a is being replaced with \.

The same thing is wrong, if we use the replaceAll() method as follows.

System.out.println(a.replaceAll("/", "\\"));

It causes the exception java.lang.StringIndexOutOfBoundsException to be thrown. It requires two additional backslashes \ like the following, since replaceAll() uses a regex which is not the case with the replace() method.

System.out.println(a.replaceAll("/", "\\\\"));

The only question is why does this method when used with only two slashes like this a.replaceAll("/", "\\") throw java.lang.StringIndexOutOfBoundsException?

2 Answers
2

Note that backslashes (\) and dollar signs ($) in the replacement string may cause the results to be different than if it were being treated as a literal replacement string; see Matcher.replaceAll. Use Matcher.quoteReplacement(java.lang.String) to suppress the special meaning of these characters, if desired.

Why does this method when used with only two slashes like this
a.replaceAll("/", "\") throw
java.lang.StringIndexOutOfBoundsException?

As you know, \ is a metacharacter in regex. When you use \ in regex, it is always followed by another character e.g. \d or \s.

Your java.lang.StringIndexOutOfBoundsException exception is coming when it tries to evaluate the pattern string ITSELF i.e. \\ and it doesn't find a following character, which is mandatory in this case. This is not coming on the argument string a --> abc/xyz as It tries to do below: